Views: 4 Author: Site Editor Publish Time: 2022-08-17 Origin: Site
Parts inspection is an important part of the process of mechanical maintenance, machinery and parts through the inspection and determine its technical condition and the process measures to be taken, and then, through the inspection and determine the technical quality after repair.
1. Main contents of parts inspection
In mechanical maintenance, parts are generally checked one by one, the main content can be divided into the following aspects:
1) Check the geometric accuracy of parts
Geometric accuracy includes dimensional accuracy and shape position accuracy, but sometimes the maintenance work is not the pursuit of the geometric size of a single part, but the requirement of relative accuracy, which is often an important part of the inspection work. Shape and position accuracy in maintenance are common roundness, cylindricity, concentricity, coaxiality, parallelism and perpendicularity.
2) Surface quality inspection
The inspection of the surface quality of the parts in the maintenance work is not limited to the inspection of the surface finish, but the inspection of the surface of the used parts whether there are scratches, burning and pulling defects.
3) Inspection of mechanical properties
According to the characteristics of mechanical maintenance, in addition to the mechanical properties of the parts of the material in the hardness of a check, other indicators are generally not checked, but the parts of the manufacturing and maintenance process encountered some performance, such as balance, spring stiffness, etc., cannot be ignored.
4) Inspection of hidden defects
In the manufacturing process, there may be original defects such as slag inclusion and cavity inside the parts, and microscopic cracks may occur in the use process. These defects cannot be found directly from the general observation and measurement, but it may have serious consequences to the machinery, therefore, in the mechanical maintenance, must have a purpose to some parts of the comprehensive inspection.
2. Method of parts inspection
There are many ways to inspect parts, and new inspection techniques are developing with each passing day. However, from the actual work of mechanical maintenance, it can be summarized into the following aspects:
1) Sensory examination
This is a way to identify the technical condition of parts only by the intuitive feeling of inspectors without checking equipment. This method is simple and easy to identify the defects of a large number of disassembled parts in mechanical maintenance. However, this method cannot be used to check the parts with high precision, and the inspectors are required to have rich experience.
2) Instrument and tool inspection method
A great deal of inspection work is carried out with instruments and tools. Due to the different principles and types of instruments and tools, it can be divided into general measuring tools, special measuring tools, mechanical instruments and meters, optical instruments, electronic instruments and so on.
3) Physical inspection method
This is a method to detect the technical condition of parts by using physical quantities such as electricity, magnetism, light, sound and heat through the changes caused by the workpiece. The realization of this method is also combined with instrument and tool inspection method. This method is usually used to check hidden defects inside the part without damaging the part itself, now commonly known as nondestructive testing. In recent years, the technology of nondestructive testing is developing day by day. Now the magnetic powder method, osmotic method, ultrasonic and ray method are widely used in production.
3. Feel check of parts
1) Visual inspection
Visual inspection of the main contents of the sensory inspection, such as parts of the fracture and macro cracks, obvious bending and distortion, parts of the surface of the burn and abrasion, serious wear and tear, usually can be directly identified with the naked eye. In order to improve the accuracy of visual inspection, magnifying glass can be used in some cases. In order to make up for the lack of visual inspection of some walls, the endoscope with light conduction fiber can be used for inspection.
2) Auditory examination
The method of judging the defects of mechanical parts by the hearing ability of the human ear is a long-standing inspection method. The routine inspection of rolling stock has been done this way for decades. When the inspection of the workpiece is knocked, when the parts without defects, the sound is clear, and when there is an internal shrinkage, the sound is low, if the internal crack, the voice hoarse, therefore, according to different sounds, you can judge whether the parts have defects.
3) Tactile examination
Touch the surface of the part with your hand to feel its surface condition. Relative shaking of the fit can feel its fit condition. Machinery in operation, through the touch of its parts, can feel its heating condition, so as to judge the state of its mechanism.
4. Measures to ensure the quality of parts inspection
1) Strict mastery of technical standards
Most mechanical parts and fittings have specified technical standards, which is the main basis for inspection work, in the absence of reliable basis for the need to modify the standards, these standards must be strictly observed, never allow to lower the standard, and put unqualified parts into use.
2) Select the inspection equipment according to the requirements of the inspection object
In addition to selecting the inspection equipment according to the nature and scope of the inspection items, special attention should be paid to the requirements of accuracy. For example, in length measurement, when the accuracy is required in the range of 1mm, the ruler can be used; When the accuracy is required in the range of 0.1mm, the vernier calipers are generally used; When the accuracy is required in 0.01mm accuracy, you need to use micrometer, dial gauge; When the accuracy of 0.001mm is required, a comparator is needed. If the precision of the device is lower than the precision required by the measured object, it cannot meet the quality inspection requirements. Precautions must be taken to prevent this.
3) Improve the technical level of inspection operation
The technical level of inspection operation directly affects the inspection accuracy, whether it is the self-inspection of maintenance personnel or full-time inspection personnel, it requires the operator to skillfully master the inspection equipment used and clear inspection object inspection requirements. Therefore, attention should be paid to the improvement of inspection technology, special training should be carried out for the use of special and important inspection equipment, and a variety of inspectors should be relatively stable.
4) Reduce inspection errors
Errors inevitably exist in any inspection results, and their effects are manifold. Therefore, we should prevent and eliminate them from the following aspects:
▶ Inspection equipment has its own accuracy level, it is necessary to calibrate it regularly, and pay attention to maintenance and storage to keep it accurate.
▶ Correct the error caused by temperature. Among the environmental factors that affect the inspection accuracy, the temperature has the biggest influence. For example, the effect of linear expansion in length inspection, the sex change caused by temperature transformation in electronic devices, etc., should be corrected in more precise measurement.
▶ Errors caused by improper operation or inaccurate reading are mostly accidental errors, so you can take the average of multiple measurements, which can greatly reduce the degree of error.
5) Establish and improve reasonable inspection rules and regulations
Reasonable inspection system is to do a good job of the inspection of the organization guarantee, to establish the post responsibility system, clear responsibility, everyone check, and suggest a certain acceptance and handover system and measurement calibration system.